U.S. patent application number 14/918314 was filed with the patent office on 2016-04-21 for process of removing heat.
The applicant listed for this patent is Velocys Technologies Limited. Invention is credited to John DOLAN, Ivan Phillip GREAGER, Roger Allen HARRIS, Steven Claude LeVINESS, Dennis PARKER, Jasmeer Jaichland RAMLAL, Andre Peter STEYNBERG.
Application Number | 20160107962 14/918314 |
Document ID | / |
Family ID | 54545382 |
Filed Date | 2016-04-21 |
United States Patent
Application |
20160107962 |
Kind Code |
A1 |
GREAGER; Ivan Phillip ; et
al. |
April 21, 2016 |
PROCESS OF REMOVING HEAT
Abstract
The present invention provides an improved process for removing
heat from an exothermic reaction. In particular, the present
invention provides a process wherein heat can be removed from
multiple reaction trains using a common coolant system.
Inventors: |
GREAGER; Ivan Phillip;
(Katy, TX) ; LeVINESS; Steven Claude; (Houston,
TX) ; HARRIS; Roger Allen; (Dublin, OH) ;
STEYNBERG; Andre Peter; (Dublin, OH) ; RAMLAL;
Jasmeer Jaichland; (Katy, TX) ; PARKER; Dennis;
(Houston, TX) ; DOLAN; John; (Tulsa, OK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Velocys Technologies Limited |
Abingdon |
|
GB |
|
|
Family ID: |
54545382 |
Appl. No.: |
14/918314 |
Filed: |
October 20, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62066233 |
Oct 20, 2014 |
|
|
|
Current U.S.
Class: |
518/706 |
Current CPC
Class: |
B01J 2219/00164
20130101; B01J 2219/00186 20130101; B01J 2208/00539 20130101; B01J
2208/00106 20130101; C10G 2/34 20130101; B01J 19/0013 20130101;
C07C 29/1512 20130101; B01J 2219/00038 20130101; B01J 2208/00548
20130101; B01J 2208/00628 20130101; C10G 2/32 20130101; B01J
2219/00162 20130101; B01J 2219/00074 20130101; Y02P 20/582
20151101; B01J 2208/00637 20130101; B01J 2219/0004 20130101; B01J
8/001 20130101; B01J 2219/0002 20130101 |
International
Class: |
C07C 29/151 20060101
C07C029/151; C10G 2/00 20060101 C10G002/00 |
Claims
1. A method for removing heat from an exothermic reaction: (a)
dividing a reactant feed stream into at least two separate reactant
substreams; (b) feeding each reactant substream into a separate
reaction train which comprises a reactor; (c) feeding a coolant
stream from a common coolant reservoir into each reactor; (d)
performing the exothermic reaction in the reactor to produce
reaction products and coolant to which heat has been transferred;
(e) feeding the coolant to which heat has been transferred from
each reaction train to a single common reservoir in which the heat
is removed from the coolant; (f) feeding the coolant from which the
heat has been removed in step (e) back into step (c), wherein: each
of the reactors in step (b) are operated at the same temperature
and pressure; and the progress of the exothermic reaction in each
reactor is controlled by adjusting the flow rate of the reactant
substream through the reaction train of which the reactor forms a
part and/or by adjusting the composition of the reactant substream
which is fed into each reaction train.
2. (canceled)
3. (canceled)
4. The method according to claim 1, wherein in step (c) the coolant
from the common coolant system is fed to two of the reaction trains
and a separate second coolant stream is fed to the third reaction
train and wherein the second coolant stream is fed to a second
reservoir in step (e).
5. The method according to claim 1, wherein the reactors are
microchannel reactors.
6. The method according to claim 1, wherein the coolant is one
which at least partially vaporizes as a consequence of the transfer
of heat from the exothermic reaction.
7. (canceled)
8. The method according to claim 6, wherein the common coolant
reservoir is a steam drum.
9. The method according to claim 8, wherein the steam drum is
operated at a temperature of about 100 to 300.degree. C. and a
pressure of 100 to 3400 kPa
10. The method according to claim 8, wherein the exothermic
reaction is a Fischer Tropsch process and the steam drum is
operated at a temperature of about 200 to 225.degree. C. and a
pressure of about 1200 to 2600 kPa, preferably the steam drum is
operated at a temperature of about 200 to 220.degree. C. and a
pressure of about 1700 to 1900 kPa.
11. (canceled)
12. The method according to 1, wherein the common coolant reservoir
comprises a heat exchanger.
13. The method according to claim 1, wherein the exothermic
reaction is selected from the group consisting of a Fischer-Tropsch
reaction, methanol production and ethylene oxide production.
14. (canceled)
15. The method according to claim 1, wherein the exothermic
reaction is a Fischer-Tropsch reaction, the reactant feedstream
comprises syngas and the reaction products are hydrocarbon
products.
16. A method according to claim 1, wherein a reaction train is
isolated by: (i) providing a second coolant circulation system
associated with a second coolant reservoir; (ii) redirecting the
coolant to which heat has been transferred from the reaction train
to be isolated to the second coolant reservoir; and then (iii)
stopping the feed of coolant in step (c) to the reaction train to
be isolated while simultaneously initiating the feed of a second
coolant from the second coolant reservoir to the reaction train to
be isolated.
17. The method according to claim 16, wherein the reactor or
reactors in the isolated reaction train comprise catalyst which is
regenerated while the reaction train is isolated.
18. The method according to claim 16, wherein an isolated reaction
train is reintroduced by: (iv) reintroducing the coolant stream in
step (c) to the isolated reaction train while simultaneously
stopping the feed of second coolant from the second reservoir to
the isolated reaction train; (v) running the process until the
operating conditions of the reactor in the isolated reaction train
match those of the reactors which were not isolated; and then (vi)
redirecting the coolant to which heat has been transferred from the
isolated reaction train to the single common reservoir.
19. (canceled)
20. The method according to claim 16, wherein the second coolant is
different from the coolant in step (c).
21. A method of starting up an exothermic reaction comprising: (a)
providing at least two separate reaction trains each comprising at
least one reactor; (b) providing a common coolant circulation
system which comprises a single common reservoir comprising a
coolant which is fed into each reaction train; (c) starting
circulation of the coolant to each reaction train; (d) increasing
the pressure the reactors to a desired reaction pressure; (e)
feeding a reactant feedstream into each reaction train; (f)
increasing the temperature of the single common reservoir while
adjusting the GHSV of the reactant feedstreams through each
reaction train to obtain the desired extent of exothermic
reaction.
22. A method of isolating a reaction train from an exothermic
reaction process circuit which comprises multiple reaction trains
to which a first coolant is fed from a common first coolant
reservoir and wherein each reaction train comprises a reactor to
which a reactant substream is fed, comprising: performing the
exothermic reaction in the reactor to produce reaction products and
first coolant to which heat has been transferred; providing a
second coolant circulation system associated with a second coolant
reservoir; redirecting the first coolant to which heat has been
transferred from the reaction train to be isolated to the second
coolant reservoir; and then stopping the feed of the first coolant
to the reaction train to be isolated while simultaneously
initiating the feed of the second coolant from the second coolant
reservoir to the reaction train to be isolated.
23. The method according to claim 22, wherein the first coolant and
the second coolant are the same.
24. The method according to claim 22, wherein the first coolant and
the second coolant are different.
25. (canceled)
26. A method for removing heat from an exothermic reaction
comprising: (a) dividing a reactant feed stream into at least two
separate reactant substreams; (b) feeding each reactant substream
into a separate reaction train which comprises a reactor; (c)
feeding a coolant stream from a common coolant reservoir into each
reactor; (d) performing the exothermic reaction in the reactor to
produce reaction products and coolant to which heat has been
transferred; (e) feeding the coolant to which heat has been
transferred from each reaction train to a single common reservoir
in which the heat is removed from the coolant; (f) feeding the
coolant from which the heat has been removed in step (e) back into
step (c), wherein: the coolant is a fluid which has a boiling point
lower than the exothermic reaction temperature; the coolant to
which heat has been transferred in steps (d) and (e) is a two phase
coolant; and the progress of the exothermic reaction in each
reactor is controlled by adjusting the pressure of the two phase
coolant.
27. (canceled)
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of priority U.S.
Provisional Patent Application Ser. No. 62/066,233, filed Oct. 20,
2014.
[0002] The present invention provides an improved process for
removing heat from an exothermic reaction. In particular, the
present invention provides a process wherein heat can be removed
from multiple reaction trains using a common coolant system.
BACKGROUND
[0003] A number of commercially useful reactions are exothermic in
nature and generate large amounts of heat which needs to be
removed. On an industrial scale, for many reactions, it is possible
to remove the heat of reaction in the form of a circulating fluid,
such as water, which is raised for steam, which can then be used
for another purpose, for example, for generating power.
[0004] An example of such a reaction is the Fischer Tropsch (FT)
reaction which converts synthesis gas (syngas) to linear
hydrocarbons. The heat of reaction may be removed by partially
vaporising boiler feed water (BFW) which is introduced into thermal
contact with and receives heat given off by the exothermic FT
reaction vessel, tubes, or channels wherein the FT catalyst is
contained and the reaction with syngas takes place. Temperature is
one of the most critical operating parameters of the FT reaction,
controlling the carbon monoxide conversion present in the syngas
(per pass CO conversion), in addition to the length of hydrocarbon
chains synthesized (selectivity).
[0005] The temperature of the coolant is selected to provide the
desired cooling capacity for the reaction. In the case where
vaporisation of water is used to cool the reaction, the temperature
of the coolant is controlled by the pressure at which the steam is
generated. Coolant which is partially vaporised as a consequence of
the exothermic reaction is passed from a reactor to a reservoir,
essentially a steam drum, where the vapour and liquid are
separated. The vapour (steam) may be further used for heating or
power generation. The liquid may be used further in the process or
treated and/or recirculated as a coolant in the process. The
pressure at which the steam drum is operated dictates the
saturation temperature of the liquid, which is then recycled back
into the reactor as coolant.
[0006] In an industrial process, there is always a drive to
maximize the production capacity of a reaction train in order to
exploit economics of scale to minimize unit cost of production. The
practical limit of production capacity of a single reaction train
may be driven by the maximum size of major equipment or other
factors. Thus, in order to meet the overall desired production
capacity of a facility, multiple reaction trains may be required.
When multiple reaction trains are used, it is commonly desired to
optimize the output and maximize the ease of operation of each
reaction train used with the associated duplication of equipment
for independent operation.
[0007] In the case of a conventional exothermic catalytic process,
in particular, where the activity of the catalyst declines over
time, each reaction train is designed to operate independently at
maximum production capacity, with an operating strategy for
different reactor temperatures in different trains as the reaction
catalyst activity declines over time and is compensated for by
increasing the reaction temperature. In this case, the coolant
temperature profiles may be different between multiple trains in
order to optimize production. In the case of a process cooled by
vaporisation of water, such as a Fischer-Tropsch (FT) process,
reaction temperature is controlled by the pressure of the resulting
steam, which is typically sent to a separate vessel ("steam drum")
in which the pressure of the steam is controlled. In this case, the
temperature and pressure of the steam drum may be different at any
point in time for each reaction train. To date, the FT process has
been designed so as to utilise a single steam drum per reaction
train. This means that the reaction temperature of each reaction
train can be controlled by the operating pressure of the associated
single steam drum. A similar approach has been adopted in other
exothermic industrial processes where the heat of reaction can be
controlled by a recirculating coolant, such as the generation of
steam from water.
SUMMARY OF INVENTION
[0008] For industrial processes, there is always a drive to
optimise the process from an economic perspective. Any change which
can be made to reduce costs while maintaining an acceptable yield,
conversion and/or selectivity is a major positive in this
field.
[0009] It is with this in mind that the inventors have surprisingly
found a way of obtaining a significant economical benefit when
operating an exothermic process in which the reaction temperature
can be controlled by the transfer of heat to a recirculating
coolant. More specifically, the present inventors have found that
even where there are multiple reaction trains, it is possible to
remove the heat of reaction using a single common coolant reservoir
rather than using a separate coolant reservoir for each reaction
train. This greatly reduces the amount of equipment which is
required thus significantly reducing costs.
[0010] However, it is entirely counter-intuitive that making this
change will bring economical benefits which outweigh the reduction
in output associated with separate temperature control of different
reaction trains. Prior to this invention, the perceived wisdom in
the field has been that it is necessary to include a separate
coolant reservoir for each reaction train. More specifically, the
impetus has been optimize the production capacity of each reaction
train by individually controlling the reaction temperature in each
reaction train, which may vary between trains due to differences in
operating history, including such factors as catalyst deactivation,
scheduled or unscheduled maintenance, and optimization of on-stream
factors by ensuring that reactor trains can be operated
independently.
[0011] For exothermic reactions, such as the FT reaction, where
temperature is a critical operating parameter, it is surprising
that it is still possible to obtain acceptable conversions and
selectivities when using a single coolant reservoir as it means
that all of the reaction trains must be operated at the same
temperature and pressure, specifically that which is dictated by
the single common coolant reservoir. However, the present inventors
have found that the performance of the exothermic reaction in each
reaction train can alternatively be controlled by altering the flow
rate of the reactants through the reaction train whilst maintaining
a common coolant reservoir condition of temperature and pressure.
Thus, it is possible to control each reaction train individually,
as is possible using conventional methods.
[0012] As used herein, the term "same temperature and pressure"
means a deviation of .+-.10 psi or less in pressure and
.+-.10.degree. C. or less in temperature.
[0013] Accordingly, the present invention provides a method for
removing heat from an exothermic reaction comprising: [0014] (a)
dividing a reactant feed stream into at least two separate reactant
substreams; [0015] (b) feeding each reactant substream into a
separate reaction train which comprises a reactor; [0016] (c)
feeding a coolant stream from a common coolant reservoir into each
reactor; [0017] (d) performing the exothermic reaction in the
reactor to produce reaction products and coolant to which heat has
been transferred; [0018] (e) feeding the coolant to which heat has
been transferred from each reaction train to a single common
reservoir in which the heat is removed from the coolant; [0019] (f)
feeding the coolant from which the heat has been removed in step
(e) back into step (c), wherein: [0020] each of the reactors in
step (b) are operated at the same temperature and pressure; and
[0021] the progress of the exothermic reaction in each reactor is
controlled by adjusting the flow rate of the reactant substream
through the reaction train of which the reactor forms a part and/or
by adjusting the composition of the reactant substream which is fed
into each reaction train.
[0022] Thus, it is clear that, although the process involves the
use of multiple reaction trains, the coolant to which heat has been
transferred from each reaction train is passed to a single common
coolant reservoir. Instead of using temperature as a key control,
the progress of the exothermic reaction in each reactor is
controlled by adjusting the flow rate of the reaction train or by
adjusting the composition of the reactant substream which is fed to
each reactor. Advantageously, the process of the present invention
reduces the amount of equipment which is required, hence reducing
the associated costs.
[0023] A further advantage of the method of the present invention
is that where there are at least three reaction trains, it is
possible to isolate and then subsequently reintroduce one of the
reaction trains from the process while having minimal impact on the
operating conditions of the remaining reaction trains. This means
that a reaction train can be isolated for catalyst regeneration or
reloading without having to stop the whole process. Again, this has
a significant economic advantage.
[0024] Steps (a)-(f)
[0025] Step (a)
[0026] In the first step (step (a)) of the method of the present
invention, a reactant feedstream is divided into at least two
reactant substreams and each substream is then fed to a separate
reaction train. Separating the reactant feedstream in this way
ensures that the extent of reaction which occurs is maximised.
[0027] In one embodiment, the reactant feedstream is divided into
at least 3, 4, 5, 6, 7, 8, 9, 10, 11, etc. feedstreams. In this
regard, the only limitation on the number of substreams into which
the reactant feedstream is divided is the complexity (and cost) of
the resulting apparatus. The greater the number of reactant
substreams, and hence reaction trains, the more straightforward it
becomes to isolate one of the reaction trains while having minimal
impact on the reaction trains which remain in operation. Typically,
the reactant feedstream is divided into between 2 and 8
feedstreams.
[0028] The nature of the reactant feedstream will depend on the
nature of the exothermic reaction. The terms "exothermic reaction"
are used to describe a chemical reaction which produces heat. In
particular, the method of the present invention is useful for any
exothermic reaction in which the heat of reaction can be controlled
by the transfer of heat to a coolant Examples of suitable
exothermic reactions include the Fischer-Tropsch process, methanol
production, ethylene oxide production, dimethyl ether (DME)
production, vinyl acetate (VAM) production, hydroprocessing
including hydrotreating, hydrocracking, oxidations, including
partial oxidations, oxidative coupling, alkane oxidation,
alkylation, isomerization, ammonia synthesis, water-gas-shift and
hydrogenation. The exothermic reactions with which the present
invention is concerned are well known and well documented such that
the skilled person would be familiar with suitable reactants and
reaction conditions.
[0029] The method of the present invention is particularly
applicable to heterogeneously catalysed reactions where the
activity of the catalyst decreases with time. For such reactions,
conventionally, it would have been necessary to increase
temperature to maintain output but the method of the present
invention provides a way in which this can be avoided.
[0030] Where the exothermic reaction is a Fischer-Tropsch reaction,
the reactant feedstream will comprise a gaseous mixture that
contains CO and H.sub.2. This mixture is often referred to as
"synthesis gas" or "syngas". The reactant feedstream may comprise
H.sub.2 and CO with a molar ratio of H.sub.2 to CO in the range
from about 1:1 to about 4:1, more preferably 1.4:1 to about 2.1:1,
or from about 1.5:1 to about 2.1:1, or from about 1.6:1 to about
2:1, or from about 1.6:1 to about 1.9:1. The reactant feedstream
may be comprised entirely of fresh synthesis gas or may
alternatively comprise a mixture of fresh synthesis gas and
recycled tail gas (which also contains CO and H.sub.2). In one
embodiment, the reactant feedstream may comprise 0 to 50%,
alternatively 4 to 15% by weight of inert components (i.e.
components which are not CO or H.sub.2).
[0031] Similarly, where the exothermic reaction is methanol
production, the reactant feedstream will comprise synthesis gas. In
this case, the reactant feedstream may comprise H.sub.2 and CO with
a molar ratio of H.sub.2 to CO in the range from 0.5 to 4,
alternatively from 1 to 2.5. The reactant feedstream may be
comprised entirely of fresh synthesis gas or may alternatively
comprise a mixture of fresh synthesis gas and recycled tail gas
(which also comprises CO and H.sub.2). In one embodiment, the
reactant feedstream may comprise 0 to 50%, alternatively 4 to 15%
by weight of inert components (i.e. components which are not CO or
H.sub.2 e.g. N.sub.2, CO.sub.2 etc).
[0032] As used herein, the term "tail gas" means the gas stream
leaving the reactor following the exothermic reaction. For example,
where the exothermic reaction is a Fischer-Tropsch reaction, the
tail gas comprises unconverted syngas, vapor-phase by-products of
the Fischer-Tropsch reaction and inert components.
[0033] Where the exothermic reaction is ethylene oxide production,
it is generally produced by the oxidation of ethylene using oxygen
over a catalyst (typically a silver catalyst) and the reactant
feedstream will comprise a mixture of ethylene and oxygen. The
reactant feedstream may comprise ethylene and oxygen with a molar
ratio of ethylene to oxygen of less than about 4:1, in one
embodiment less than about 3:1. The molar ratio of ethylene to
oxygen may be in the range from 0.2:1 to about 4:1 or from about
0.5:1 to about 3:1 or from about 1:1 to about 3:1.
[0034] In an embodiment where the exothermic reaction is dimethyl
ether DME production, where the DME is produced by direct reaction
of syngas to DME or by dehydration of methanol over a dehydration
catalyst, the reactant feedstream comprises methanol.
Alternatively, the DME may be produced by a process that integrates
methanol synthesis and dehydration into a single reactor, in which
case the reactant feed stream comprises synthesis gas.
[0035] In one embodiment, the exothermic reaction is a
hydrocracking reaction. Hydrocracking requires the reaction between
hydrogen and one or more hydrocarbon reactants. The hydrocarbons
may comprise any hydrocarbon that can be hydrocracked including
saturated aliphatic compounds (e.g. alkanes), unsaturated aliphatic
compounds (e.g. alkenes, alkynes), hydrocarbyl (e.g. alkyl)
substituted aromatic compounds, hydrocarbylene (e.g. alkylene)
substituted aromatic compounds and the like. In this case, the
reactant feedstream may comprise one or more hydrocarbon reactants
that may vary from naphtha to heavy crude oil residual fractions.
In this regard, the feed composition may have a 5% by volume
boiling point above about 175.degree. C., and in one embodiment
above about 205.degree. C. In one embodiment, at least about 90% by
volume of the feed composition may fall within the boiling point
range of about 150.degree. C. to about 570.degree. C., and in one
embodiment from about 320.degree. C. to about 540.degree. C. The
feed composition nay comprise one or more petroleum fractions such
as atmospheric and vacuum gas oils (AGO and VGO). The feed
composition may comprise one or more mineral or synthetic oils, or
a mixture of one or more fractions thereof. The feed composition
may comprise one or more straight run gas oils, vacuum gas oils,
demetallized oils, deasphalted vacuum residues, coker distillates,
cat cracker distillates, shale oil, tar sand oil, coal liquids, or
a mixture of two or more thereof, and the like. The ratio of
hydrogen to hydrocarbon reactant in the reactant substream which is
fed to the reaction train may be in the range from about 10 to
about 1000 standard cubic centimetres (sccm) of hydrogen per cubic
centimetres (ccm) of hydrocarbon reactant, or in the range from
about 100 to about 500 sccm/cm.
[0036] Where the exothermic reaction is VAM production, the
reactant feedstream may comprise ethylene, acetic acid and
dioxygen. In one embodiment, the ratio of ethylene to acetic acid
to dioxygen in the reactant feedstream may be in the range from
about 6:3:1 to about 2:2:1.
[0037] Where the exothermic reaction is oxidation of a hydrocarbon
reactant to an oxygenate or a nitrile, the reactant feedstream may
comprise a hydrocarbon reactant, oxygen or a source of oxygen and
optionally ammonia. The term "hydrocarbon reactant" refers to any
hydrocarbon compound that is capable of undergoing an oxidation or
ammoxidation reaction and is a fluid at the temperature and
pressure at which the reactor is operated. Examples include
saturated aliphatic compounds (e.g. alkanes), unsaturated aliphatic
compounds (e.g. monoenes, polyenes), aldehydes, alkyl substituted
aromatic compounds, alkylene substituted aromatic compounds. The
term "oxygenate" refers to a hydrocarbon product which contains at
least one oxygen atom (CO and CO.sub.2 are excluded). Examples
include alcohols (e.g. methanol, ethyl alcohol), epoxides (e.g.
ethylene oxide), aldehydes (e.g. formaldehydes, acrolein),
carboxylic acids (e.g. acetic acid, acrylic acid), carboxylic acid
anhydrides (e.g. maleic anhydride), esters (e.g. vinyl acetate).
The mole ratio of the hydrocarbon reactant to oxygen may be in the
range from about 0.2:1 to about 8:1 or from about 0.5:1 to about
4:1, or from about 1:1 to about 3:1. The ammonia may be obtained
from any source. Where it is present, the mole ratio of the
hydrocarbon reactant to ammonia may range from about 0.5:1 to about
5:1 or from about 0.5:1 to about 2:1.
[0038] In one embodiment, the exothermic reaction is the oxidation
of methanol to formaldehyde. In this embodiment, the reactant
feedstream comprises methanol and oxygen.
[0039] Step (b)
[0040] In step (b) of the method of the present invention, each
reactant substream is fed into a separate reaction train. Each
reaction train comprises at least one reactor. In order to maximise
the extent of reaction, it may be advantageous for each reactant
train to comprise multiple reactors. Where multiple reactors are
present, they may be arranged in series or in parallel. Preferably
the multiple reactors are arranged in parallel. In some
embodiments, for example where the exothermic reaction is a FT
reaction, the multiple reactors are arranged in parallel.
[0041] The nature of the reactors is not limited. In one
embodiment, the reactor may be selected from the group consisting
of a conventional fixed bed reactor, a fluidised bed reactor, a
slurry phase reactor and a microreactor.
[0042] The skilled person will be familiar with suitable
conventional fixed bed reactors. Commercial conventional fixed bed
reactors are made up of multiple, in some cases hundreds or
thousands of long (up to 10 metres), narrow reactor tubes which are
welded onto "tube plates" and which are filled with packing
material which comprises catalyst, thus forming a bed of catalyst
through which the reactant substream flows. The tubes may have a
diameter in the range from 20 to 50 mm. The catalyst may be in the
form of pellets having a diameter in the range from 1 to 5 mm. The
catalyst particles may be designed to be uneven shapes in order to
reduce their packing efficiency within the reactor tubes and
prevent undue pressure drop. The length of the reactor tubes means
that the conversion of the exothermic reaction is maximised because
the reactant substream is in contact with the catalyst for an
increased time.
[0043] The skilled person will also be familiar with fluidised bed
reactors. There are two types of fluidised bed reactor. In a fixed
fluidised bed reactor (FFB), the catalyst bed is contained within
the reactor vessel. In a circulating fluidised bed (CFB), the
catalyst is entrained in the gas flow and is carried around a
loop.
[0044] In fixed fluidised bed reactors, the reactant substream is
passed through the catalyst bed (comprised of catalyst particles)
at a sufficient velocity to cause the bed to fluidise. The catalyst
particles are typically much smaller than those used in a fixed bed
reactor in order to enable them to be fluidised at reasonable gas
velocities. Within the top of the reactor, cyclones disengage the
catalyst particles and return them to the bed while the product
stream flows through the condensing train. Cooling coils are
arranged with the reactor to remove heat. The suspended particles
are in intimate contact with the gas stream and the cooling coils.
In a fixed fluidised bed reactor, the catalyst particles are moving
at high velocities and experience regular collisions which causes
them to physically break down into a powder. This means that the
catalyst particles have to be replaced on a continuous basis.
[0045] As the skilled person will be aware, in a slurry phase
reactor, the reactant substream is passed through a slurry made up
of a powdered supported catalyst. The catalyst typically comprises
solid catalyst particles having a diameter in the range from 0.05
to 0.3 mm. Where the reactant stream is a gas which is introduced
at the bottom of the reactor and then rises up through the slurry,
the reactor is known as a bubble column reactor. Slurry phase
reactors are advantageous because they provide excellent
temperature control and close to isothermal operation with no
temperature gradients. However, liquid products formed in the
reactor must be filtered after removal from the slurry bed in order
to ensure that all of the catalyst particles have been removed.
[0046] In one embodiment, the reactor is a microchannel reactor.
The term "microchannel reactor" refers to an apparatus comprising
one or more process microchannels wherein a reaction process is
conducted. In particular, the microchannel reactor may comprise at
least one, preferably a plurality of process microchannels in
thermal contact with at least one, preferably a plurality of heat
exchange channels. Where a catalyst is present, it is contained
within the process microchannels.
[0047] Examples of suitable microchannel reactors are described in
WO2014/026204, the contents of which is incorporated herein by
reference.
[0048] In particular, the microchannel reactor may comprise one or
more slots for receiving one or more catalyst inserts (e.g., one or
more fins or fin assemblies, one or more corrugated inserts, etc.)
wherein the process microchannels comprise the slots, are
positioned in the catalyst inserts, and/or comprise openings formed
by the walls of the slots and the inserts. When two or more process
microchannels are used, the process microchannels may be operated
in parallel. The microchannel reactor may include a header or
manifold assembly for providing for the flow of fluid into the one
or more process microchannels, and a footer or manifold assembly
providing for the flow of fluid out of the one or more process
microchannels. The microchannel reactor may comprise one or more
heat exchange channels adjacent to and/or in thermal contact with
the one or more process microchannels. The heat exchange channels
may provide cooling for the fluids in the process microchannels.
The heat exchange channels may be microchannels. The microchannel
reactor may include a header or manifold assembly for providing for
the flow of heat exchange fluid into the heat exchange channels,
and a footer or manifold assembly providing for the flow of heat
exchange fluid out of the heat exchange channels.
[0049] The term "microchannel" refers to a channel having at least
one internal dimension of height or width of up to about 10
millimeters (mm), and in one embodiment up to about 5 mm, in one
embodiment up to about 2 mm, in one embodiment up to about 1 mm.
The microchannel may comprise at least one inlet and at least one
outlet wherein the at least one inlet is distinct from the at least
one outlet. The microchannel may not be merely an orifice. The
microchannel may not be merely a channel through a zeolite or a
mesoporous material. The length of the microchannel may be at least
about two times the height or width, and in one embodiment at least
about five times the height or width, in one embodiment at least
about ten times the height or width. The internal height or width
of the microchannel may be in the range of about 0.05 to about 10
mm, or from about 0.05 to about 5 mm, or from about 0.05 to about 2
mm, or from about 0.05 to about 1.5 mm, or from about 0.05 to about
1 mm, or from about 0.05 to about 0.75 mm, or from about 0.05 to
about 0.5 mm, or from about 1 to about 10 mm, or from about 2 to
about 8 mm, or from about 3 to about 7 mm. The other internal
dimension of height or width may be of any dimension, for example,
up to about 3 meters, or about 0.01 to about 3 meters, and in one
embodiment about 0.1 to about 3 meters, or about 1 to about 10 mm,
or from about 2 to about 8 mm, or from about 3 to about 7 mm. The
length of the microchannel may be of any dimension, for example, up
to about 10 meters, and in one embodiment from about 0.1 to about
10 meters, and in one embodiment from about 0.2 to about 10 meters,
and in one embodiment from about 0.2 to about 6 meters, and in one
embodiment from 0.2 to about 3 meters. The microchannel may have a
cross section having any shape, for example, a square, rectangle,
circle, semi-circle, trapezoid, etc. The shape and/or size of the
cross section of the microchannel may vary over its length. For
example, the height or width may taper from a relatively large
dimension to a relatively small dimension, or vice versa, over the
length of the microchannel.
[0050] The term "adjacent" when referring to the position of one
channel relative to the position of another channel may mean
directly adjacent such that a wall or walls separate the two
channels. In one embodiment, the two channels may have a common
wall. The common wall may vary in thickness. However, "adjacent"
channels may not be separated by an intervening channel that may
interfere with heat transfer between the channels. One channel may
be adjacent to another channel over only part of the dimension of
the another channel. For example, a process microchannel may be
longer than and extend beyond one or more adjacent heat exchange
channels.
[0051] The term "thermal contact" refers to two bodies, for
example, two channels, that may or may not be in physical contact
with each other or adjacent to each other but still exchange heat
with each other. One body in thermal contact with another body may
heat or cool the other body.
[0052] The term "fluid" refers to a gas, a liquid, a mixture of a
gas and a liquid, or a gas or a liquid containing dispersed solids,
liquid droplets and/or gaseous bubbles. The droplets and/or bubbles
may be irregularly or regularly shaped and may be of similar or
different sizes.
[0053] Catalyst
[0054] The reactor may comprise a catalyst. Preferably the catalyst
is a heterogeneous catalyst. In one embodiment, the catalyst may be
in the form of particulate solids.
[0055] Where the reactor is a microchannel reactor as described
above, the catalyst may be used as a particulate solid loaded into
the process channels, or coated on interior walls of the process
microchannels or grown on interior walls of the process
microchannels. The catalyst may be supported on a support having a
flow-by configuration, a flow-through configuration or a serpentine
configuration. The catalyst may be supported on a support having
the configuration of a foam, felt, wad, fin or a combination of two
or more thereof. Alternatively, the catalyst may be in the form of
insert which may be fitted within a suitable slot within the
reactor.
[0056] The skilled person will be familiar with catalysts suitable
for performing different exothermic reactions.
[0057] In particular, where the exothermic reaction is a
Fischer-Tropsch process, preferably the catalyst may be derived
from a catalyst precursor comprising cobalt, a promoter such as Pd,
Pt, Rh, Ru, Re, Ir, Au, Ag and/or Os and a surface modified
support, wherein the surface of the support has been modified by
being treated with silica, titania, zirconia, magnesia, chromia,
alumina or a mixture of two or more thereof. In one embodiment, the
catalyst precursor may comprise a cobalt oxide, in particular
CO.sub.3O.sub.4. Suitable support materials include a refractory
metal oxide, carbide, carbon, nitride or a mixture of two or more
thereof. The support may comprise alumina, zirconia, silica,
titania, or a mixture of two or more thereof. In one embodiment,
the support may comprise a TiO.sub.2 modified silica support
wherein the support contains at least about 11% by weight
TiO.sub.2, or from about 11 to about 30% by weight TiO.sub.2, or
from about 15 to about 17% by weight TiO.sub.2, in one embodiment,
about 16% by weight TiO.sub.2. The surface of the surface-modified
support may be amorphous.
[0058] In an embodiment where the exothermic reaction is methanol
production, preferably the catalyst is a copper-based catalyst, for
example Cu/ZnO/Al.sub.2O.sub.3.
[0059] In an embodiment where the exothermic reaction is ethylene
oxide production, preferably the catalyst may comprise a metal,
metal oxide or mixed metal oxide of a metal selected from Mo, W, V,
Nb, Sb, Sn, Pt, Pd, Cs, Zr, Cr, Mg, Mn, Ni, Co, Ce or a mixture of
two or more thereof. These catalysts may also comprise one or more
alkali metals or alkaline earth metals or other transition metals,
rare earth metals or lanthanides. Elements such as P and Bi may be
present. The catalyst may be supported and, if so, useful support
materials include metal oxides (e.g. alumina, titania, zirconia),
silica, mesoporous materials, zeolites, refractory materials or
combinations of two or more thereof. In particular, the catalyst
may be any one of the catalysts disclosed in U.S. Pat. No.
5,597,773, U.S. Pat. No. 5,703,253, U.S. Pat. No. 5,705,661, U.S.
Pat. No. 6,762,311 and EP0266015, the contents of which are
incorporated herein by reference.
[0060] In an embodiment where the exothermic reaction is DME
production, the catalyst may be a blend of a methanol synthesis
catalyst, for example Cu/ZnO/Al.sub.2O.sub.3 and a dehydration
catalyst, e.g. g-Al.sub.2O.sub.3.
[0061] In an embodiment where the exothermic reaction is
hydrocracking, the catalyst may include zeolite catalysts including
beta zeolite, omega zeolite, L-zeolite, ZSM-5 zeolites and Y-type
zeolites. The hydrocracking catalyst may comprise one or more
pillared clays, MCM-41, MCM-48, HMS, or a combination of two or
more thereof. The hydrocracking catalyst may comprise Pt, Pd, Ni,
Co, Mo, W, or a combination of two or more thereof. The
hydrocracking catalyst may include a refractory inorganic oxide
such as alumina, magnesia, silica, tilania, zirconia and
silica-alumina. The hydrocracking catalyst may comprise a
hydrogenation component. Examples of suitable hydrogenation
components include metals of Group IVB and Group VIII of the
Periodic Table and compounds of such metals. Molybdenum, tungsten,
chromium, iron, cobalt, nickel, platinum, palladium, iridium,
osmium, rhoduim and ruthenium may be used as the hydrogenation
component. These catalysts are described in U.S. Pat. No. 6,312,586
B1, which is incorporated herein by reference.
[0062] In an embodiment where the exothermic reaction is
hydrotreating, the hydrotreating catalyst may be any hydrotreating
catalyst. The hydrotreating catalyst may comprise Ni, Mo, Co, W, or
combinations of two or more thereof supported on alumina. The
catalyst may comprise Mo--W/Al.sub.2O.sub.3.
[0063] In an embodiment where the exothermic reaction is the
production of VAM, the catalyst may comprise Pd, Au and, in some
embodiments, potassium acetate (KOAc). Examples of suitable
catalysts are described in U.S. Pat. No. 3,743,607, U.S. Pat. No.
3,775,342, U.S. Pat. No. 5,557,014, U.S. Pat. No. 5,990,334, U.S.
Pat. No. 5,998,659, U.S. Pat. No. 6,022,823, U.S. Pat. No.
6,057,260 and U.S. Pat. No. 6,472,556, all of which are
incorporated herein by reference. The catalysts used preferably
contain a refractory support, preferably a metal oxide such as
silica, silica-alumina, titania or zirconia. In one embodiment, the
catalyst comprises more than 2 wt % Pd, more than 4 wt % Pd, more
than 10 wt % Pd and in some embodiments, at least 12 wt % Pd.
[0064] In an embodiment where the exothermic reaction is
hydrocarbon oxidation, the catalyst may comprise a metal, metal
oxide or mixed metal oxide of a metal selected from Mo, W, V, Nb,
Sb, Sn, Pt, Pd, Cs, Zr, Cr, Mg, Mn, Ni, Co, Ce or a mixture of two
or more thereof. These catalysts may also comprise one or more
alkali metals or alkaline earth metals or other transition metals,
rare earth metals or lanthanides. Elements such as P and Bi may be
present. The catalyst may be supported and, if so, useful support
materials include metal oxides (e.g. alumina, titania, zirconia),
silica, mesoporous materials, zeolites, refractory materials or
combinations of two or more thereof.
[0065] In an embodiment where the exothermic reaction is the
oxidation of methanol to form formaldehyde, the catalyst may be a
Fe--Mo--Ox catalyst.
[0066] Step (c)
[0067] In step (c) of the method of the invention, a coolant is fed
into the reactors in each reaction train. The coolant fed into each
reaction train is derived from a common coolant reservoir. In this
regard, there is a single coolant circulation network which feeds
into all of the reaction trains. The coolant is comprised of fresh
coolant and coolant recycled from the steam drum in step (e).
[0068] Alternatively, where there are three or more reaction
trains, at least two of the reaction trains may be fed coolant in
step (c) from a single coolant circulation network while the
remaining reaction trains are fed coolant from one or more
different coolant circulation networks. In such an embodiment,
there will be multiple coolant reservoirs. However, the total
number of coolant reservoirs will always be lower than the total
number of reaction trains.
[0069] The coolant may be selected from the group consisting of a
fluid which at least partially vaporizes as a consequence of the
transfer of heat from the exothermic reaction which takes place in
the reactor and a hot oil. As will be appreciated by the skilled
person, the choice of coolant will depend on the exothermic
reaction and, in particular, the temperatures reached in the
reactor in which the exothermic reaction takes place.
[0070] The fluid which is partially vaporized may be a single
component coolant fluid, such as water, propane, butane, pentane,
hexane, ammonia, an alcohol, or a higher hydrocarbon.
Alternatively, the fluid which is partially vaporized may be a
coolant mixture comprising one or more single component fluids.
Examples of a coolant mixture include ammonia-water or a mixed
solvent.
[0071] In one embodiment, the coolant is a fluid which at least
partially vaporizes as a consequence of the transfer of heat from
the exothermic reaction which takes place in the reactor. Where
this is the case, the coolant is a fluid which has a boiling point
lower than the temperature reached in the reactor. Preferably, the
coolant is water. Where the coolant is water, the heat transferred
from the exothermic reaction causes the water to at least partially
vaporize, thus generating steam. This steam can be recovered and
used elsewhere in the process or even to produce electricity. It is
particularly preferred to use water as a coolant where the
temperature of the exothermic reaction is in the range from 80 C to
450 C, or more preferably 100 C to 300 C. Another example of
suitable coolants which fall within this group i.e. which at least
partially vaporize during the process, are organic solvents such as
those described in WO2013/055864, the contents of which is
incorporated herein by reference.
[0072] The coolant which is fed to the reactors may be at a
temperature in the range from about 40 C to about 400.degree. C.,
preferably in the range from about 100 C to about 250 C.
[0073] The coolant may either be fed to the reactors at a constant
flow or the flow may be adjusted depending upon the release of heat
which, in turn, depends on the rate at which the reactant
feedstream is fed to the reactor(s).
[0074] The coolant may be subcooled by either direct (mixing) or
indirect heat exchange to maintain the desired CO conversion rate
or product selectivity.
[0075] Where the reactor is a microchannel reactor as described
previously, the coolant is fed into the heat exchange channels
which are in thermal contact with the process channels.
[0076] Step (d)
[0077] As the reactant substream flows along the reaction train and
through the one or more reactors, it is contacted with the catalyst
and the exothermic reaction takes place (step (d)). The heat
generated by the exothermic reaction is transferred to the coolant,
thus removing the heat from the reaction. Hence, step (d) produces
reaction products and coolant to which heat has been transferred.
Where the coolant is a hot oil, it absorbs the heat by expansion
rather than by vaporization. Where the coolant is a fluid which has
a boiling point lower than the heat generated by the exothermic
reaction, it removes heat from the reaction by undergoing a partial
phase change, for example, where water is the coolant, steam is
generated.
[0078] Reaction Products
[0079] Where the exothermic reaction is a Fischer-Tropsch process,
the reaction products comprise hydrocarbons (which are
predominantly aliphatic) and water. The term "aliphatic
hydrocarbons" is used to describe an aliphatic hydrocarbon having 2
or more carbon atoms, or 3 or more carbon atoms, or 4 or more
carbon atoms, or 5 or more carbon atoms, or 6 or more carbon atoms.
The higher molecular weight aliphatic hydrocarbons may have up to
about 200 carbons atoms, up to about 150 carbons atoms, up to about
100 carbon atoms, up to about 90 carbon atoms, up to about 80
carbon atoms, up to about 70 carbon atoms, up to about 60 carbon
atoms, up to about 50 carbon, up to about 40 carbon atoms or up to
about 30 carbon atoms. Examples may include ethane, propane,
butane, pentane, hexane, octane, decane, dodecane and the like.
[0080] In an embodiment where the exothermic reaction is methanol
production, the reaction products comprise methanol, hydrogen and
water.
[0081] In an embodiment where the exothermic reaction is ethylene
oxide production, the reaction products comprise ethylene oxide,
carbon dioxide and water.
[0082] In an embodiment where the exothermic reaction is DME
production, the reaction products comprise DME and carbon
dioxide.
[0083] In an embodiment where the exothermic reaction is
hydrocracking, the reaction products comprise two or more
hydrocarbon products having lower molecular weights than the
hydrocarbon reactant.
[0084] In an embodiment where the exothermic reaction is the
production of VAM, the reaction products comprise vinyl acetate
monomer and water.
[0085] In an embodiment where the exothermic reaction is
hydrocarbon oxidation, the reaction products comprise an oxygenate
product.
[0086] In an embodiment where the exothermic reaction is
formaldehyde production, the reaction products comprise
formaldehyde.
[0087] Step (e)
[0088] In step (e), the coolant to which heat has been transferred
from each of the reaction trains is fed to a common single coolant
reservoir. In the reservoir, the heat absorbed from the exothermic
reaction is removed and the coolant is returned to its original
state. The coolant can then be recycled back into step (c).
[0089] The person skilled in the art will be familiar with suitable
reservoirs. In particular, depending on the nature of the coolant,
the reservoir may be a heat exchanger, for example where the
coolant is a hot oil. Alternatively, where the coolant is one which
has been at least partially vaporized, the reservoir may comprise a
phase separator for removing the heat in the form of a vapor. An
example of such a reservoir is a steam drum.
[0090] Where the heat of the exothermic reaction has been removed
in step (d) by partial vaporization of the coolant, the vapor and
liquid phases are separated in the reservoir, the vapor is removed
and the liquid is recycled back as coolant into step (c). In this
situation, it may be necessary to add fresh coolant to the stream
which is fed back into step (c) to compensate for the coolant which
has been lost as vapor. For example, where the coolant is water,
the reservoir is a steam drum wherein steam and water are
separated. The recovered water is recycled back into step (c) as
coolant and topped up with fresh water to compensate for the water
which has been lost in the form of steam. The steam may be
condensed and returned to the coolant system.
[0091] The conditions, in particular the pressure, under which this
single common coolant reservoir is operated dictate the saturation
temperature of the liquid which is then recycled to the reactor as
coolant and hence dictate the operating temperature and pressure of
each of the reaction trains. Where the coolant is a hot oil which
expands rather than vaporizes in response to the transfer of heat
from the exothermic reaction, it is the temperature under which the
single common coolant reservoir is operated which dictates the
operating temperature of each of the reaction trains. Hence, all of
the reactors in the method of the present invention are operated at
the same temperature and pressure.
[0092] In one embodiment, the coolant is a fluid which is partially
vaporized as a consequence of the transfer of heat from the
exothermic reaction, preferably water and the reservoir is a steam
drum.
[0093] The common single coolant reservoir may be operated at a
temperature in the range from about 25 to about 300.degree. C.,
from about 100 to about 300.degree. C., or about 200 to about
225.degree. C., or about 200 to about 220.degree. C., or about
205.degree. C. The common single coolant reservoir may be operated
at a pressure in the range from about 100 to about 15,000 kPa, or
about 100 to about 8600 kPa, or about 450 to about 4100 kPa, or
about 450 to about 3400 kPa, or about 1200 to about 2600 kPa, or
about 1200 to 2100 kPa, or about 1200 to about 1900 kPa.
[0094] In one embodiment, the common single steam drum is operated
at a temperature in the range from 100 to 300.degree. C., in one
embodiment (for example where the exothermic reaction is a FT
process) 200 to 225.degree. C., or 200 to 220.degree. C., or about
205.degree. C. and a pressure in the range from about 100 to about
8600 kPa, about 100 to about 3400 kPa, in one embodiment, about
1200 to about 2600 kPa, or about 1200 to about 2100 kPa, or about
1200 to about 1900 kPa, or about 1700 to about 1900 kPa.
[0095] Controlling the Progress of the Exothermic Reaction
[0096] The use of a common single coolant reservoir means that
temperature of the individual reaction trains (which is the usual
variable used) cannot be used to control the performance of the
exothermic reaction which is taking place in each of the reactors.
This being the case, the present inventors have surprisingly found
that it is possible to obtain an acceptable degree of control over
the different reaction trains by controlling the flow rate (or Gas
Hourly Space Velocity (GHSV)) of the reactant substream through
each reaction train.
[0097] The GHSV of the reactant substream is conventionally defined
as the volumetric flow of reactant at normal pressure and
temperature divided by the bulk volume of catalyst through which it
is flowing. The GHSV of the reactant substream can be measured by
conventional techniques, specifically by measuring the flow rate of
the reactant substream to the reactor and then by dividing this
value by the volume of the catalyst.
[0098] A means of adjusting the flow rate of the reactant substream
may be provided in at least one of the reaction trains. Preferably,
a separate means of adjusting the flow rate of the reactant
substream is provided in each of the reaction trains allowing the
flow rate of each reactant substream to be adjusted independently.
The means of adjusting the flow rate may be a valve, e.g. an
automated control valve, preferably an automated flow control
valve.
[0099] The flow rate of a reactant substream may be adjusted to
account for factors such as the deactivation of the catalyst in the
reactor present in that reaction train. Catalyst deactivation leads
to a reduction in catalytic activity over time. The method of the
present invention may be used to reduce the flow rate of the
reactants to a particular reactor in line with the deactivation of
the catalyst in order to adjust the conversion upward to compensate
for such catalyst deactivation, to ensure each reaction train meets
the desired CO conversion rate or product selectivity. The
catalysts in different reaction trains may be at different stages
of deactivation. The ability to independently adjust the flow rates
of the reactant substreams in each reaction train provides a means
to ensure that each reaction train is operating at the desired CO
conversion rate or product selectivity, regardless of any
difference in the stage of deactivation of the catalysts.
[0100] The flow rate of the reactant substream can be determined by
reference to the desired contact time of the reactants with the
catalyst. The term "contact time" refers to the volume of a
reaction zone, i.e. the space within a reactor where the exothermic
reaction occurs, divided by the volumetric flow rate of the
reactant substream at a temperature of 0.degree. C. and a pressure
of one atmosphere.
[0101] To maintain a constant reaction within a reactor,
specifically a microchannel reactor, any flow rate adjustments to a
particular reactant substream should ensure a contact time of the
reactants with the catalyst of from about 10 to about 2000
milliseconds (ms), or from about 10 ms to about 1000 ms, or from
about 20 ms to about 500 ms, or from about 200 ms to about 400 ms,
or from about 240 ms to about 350 ms.
[0102] Alternatively or in addition, the present inventors have
also found that the extent of the exothermic reaction can be
controlled by altering the composition of the reactant substream to
each reaction train. In some embodiments, the reactant substream
may be comprised of reactants obtained from different sources. For
example, in one embodiment, the reactant substream may comprise
both fresh reactants and recycled reactants. The recycled portion
of the reactant substream may have a different composition to the
fresh feed, in particular in relation to the amount of inerts which
are present. Hence, one way in which the composition of the
reactant substream may be altered is to alter the proportion of the
reactant substream which is made up from recycled reactants. In a
different embodiment, the reactant substream may be comprised of
fresh reactant and reactants which have been obtained from an
upstream process. For example, where the exothermic reaction is a
FT process, the reactant substream may comprise fresh syngas and
feed from an upstream syngas conversion convention, wherein the
feed from the upstream process will comprise a different proportion
of inert components.
[0103] A means of adjusting the composition of the reactant
substream may be provided in at least one of the reaction trains.
Preferably, a separate means of adjusting the composition of the
reactant substream is provided in each of the reaction trains
allowing the composition of the reactant substream to be adjusted
independently. The means of adjusting the composition of the
reactant substream may comprise introducing recycled reactants into
the reactant substream. The proportion of the reactant substream
which is made up from recycled reactants may be controlled by
adjusting the flow of the recycled reactants into the reactant
substream e.g. by the use of a valve, preferably an automated
control valve e.g. an automated flow control valve. Alternatively
or in addition, the flow rate of the reactant substream prior to
addition of the recycled reactants may be adjusted by the use of a
valve, preferably an automated control valve e.g. an automated flow
control valve. Alternatively, or in addition, the flow rate of the
reactant substream subsequent to addition of the recycled reactants
(i.e. the combination of the fresh and the recycled reactants) may
be adjusted by the use of a valve, preferably an automated control
valve e.g. an automated flow control valve. By controlling the flow
rate of the recycled reactants and the flow rate of at least one of
(i) the reactant substream prior to addition of the recycled
reactants and (ii) the reactant substream subsequent to addition of
the recycled reactants, it is possible to control the flow rate of
the reactants through the reactor thereby ensuring each reaction
train meets the desired CO conversion rate or product
selectivity.
[0104] In one embodiment, the progress of the exothermic reaction
in a reactor may be controlled by adjusting the flow rate of the
reactant substream through the reaction train of which the reactor
forms a part and by adjusting the composition of the reactant
substream which is fed into the same reaction train.
[0105] In a further embodiment, the progress of the exothermic
reaction in at least one reactor is controlled by adjusting the
flow rate of the reactant substream through the reaction train of
which the at least one reactor forms a part, while the progress of
the exothermic reaction in at least one further reactor is
controlled by adjusting the composition of the reactant substream
through the reaction train of which the at least one further
reactor forms a part.
[0106] Advantageously, the method of the present invention provides
a performance which is at least equivalent to that of current
processes. More specifically, where the exothermic reaction is a
Fischer-Tropsch process, the conversion of CO from the synthesis
gas in the reactant feedstream may be about 70% or higher,
preferably about 75% or higher, preferably about 80% or higher,
preferably about 85% or higher, preferably about 90% or higher,
preferably about 91% or higher, preferably about 92% or higher. In
some embodiments, the conversion may be in the range from about 88%
to about 95%, alternatively in the range from about 90% to about
94%, alternatively in the range from about 91% to about 93%. The
selectivity to methane in the reaction products may be in the range
from about 0.01% to about 15%, alternatively about 0.01% to about
10%, alternatively about 1% to about 5%, alternatively from about
3% to about 9%, alternatively from about 4% to about 8%.
[0107] Isolating an Individual Reaction Train
[0108] As described above, an advantage of the method of the
present invention, in particular where the reactant feedstream is
divided into at least three reactant substreams, is that it becomes
possible to isolate an individual reaction train from the system,
while maintaining the remaining reaction trains in an operational
state and having minimal impact upon their operation. This is
particularly advantageous where the exothermic process involves the
use of a heterogeneous catalyst, the performance of which decreases
with time such that it will, at some point, require regeneration.
It may also prove useful where reloading of the catalyst is
required.
[0109] In particular, a reaction train may be isolated by (i)
providing a second coolant circulation system associated with a
second coolant reservoir; (ii) redirecting the coolant to which
heat has been transferred from the reaction train to be isolated to
the second coolant reservoir; and then (iii) stopping the feed of
coolant in step (c) to the reaction train to be isolated while
simultaneously initiating the feed of a second coolant from the
second coolant reservoir to the reaction train to be isolated.
[0110] After step (iii), the operating conditions for the reaction
train which has been isolated from the process can be altered to
allow for regeneration of the catalyst. Alternatively or in
addition, the catalyst may be reloaded while the reaction train is
isolated.
[0111] When the regeneration (or reloading) of the catalyst has
been completed and the isolated reaction train is to be brought
back online, it is important to ensure that the steps carried out
in isolating the reaction train are performed in reverse. In this
regard, an isolated reaction train may be reintroduced by: (iv)
reintroducing the coolant stream in step (c) to the isolated
reaction train while simultaneously stopping the feed of second
coolant from the second reservoir to the isolated reaction train;
(v) running the process until the operating conditions of the
reactor in the isolated reaction train match those of the reactors
which were not isolated; and then (vi) redirecting the coolant to
which heat has been transferred from the isolated reaction train to
the single common reservoir.
[0112] By performing the steps in this order, it is possible to
ensure that the isolated reaction train can be brought back online
while having minimal impact on the operation of the reaction trains
which have remained online throughout the process.
[0113] The second coolant may be the same or different from the
coolant which is fed to the reaction trains in step (c).
[0114] Accordingly, in one aspect, the present invention provides a
method of isolating a reaction train from an exothermic reaction
process circuit which comprises multiple reaction trains to which a
first coolant is fed from a common first coolant reservoir and
wherein each reaction train comprises a reactor to which a reactant
substream is fed, comprising: [0115] performing the exothermic
reaction in the reactor to produce reaction products and [0116]
first coolant to which heat has been transferred; [0117] providing
a second coolant circulation system associated with a second
coolant reservoir; [0118] redirecting the first coolant to which
heat has been transferred from the reaction train to be isolated to
the second coolant reservoir; and then [0119] stopping the feed of
the first coolant to the reaction train to be isolated while
simultaneously initiating the feed of the second coolant from the
second coolant reservoir to the reaction train to be isolated.
[0120] The ability to be able to isolate different reaction trains
from the overall process at different times and thus have reaction
trains which have different "histories", in particular in relation
to the regeneration of the catalyst is unique to the method of the
present invention.
[0121] In a further aspect, the present invention provides a method
of reintroducing a reaction train which has been isolated from an
exothermic reaction process circuit which comprises multiple
reaction trains to which a first coolant is fed from a common
coolant reservoir, wherein each reaction train comprises a reactor
to which a reactant substream is fed and wherein: [0122] an
exothermic reaction is performed in the reactor of each reaction
train to produce [0123] reaction products and first coolant to
which heat has been transferred; and [0124] the isolated reaction
train is fed a second coolant from a second coolant reservoir, the
method comprising: [0125] stopping the feed of the second coolant
to the isolated reaction train while [0126] simultaneously
initiating a feed of first coolant to the isolated reaction train;
[0127] running the process until the operating conditions of the
reactor in the isolated [0128] reaction train match those of the
reactors which were not isolated; and then [0129] redirecting the
first coolant to which heat has been transferred from the isolated
reaction train to the common coolant reservoir.
[0130] The use of a single common coolant circulation system in
conjunction with multiple reaction trains also makes it possible to
start up the exothermic process in an efficient and straightforward
manner.
[0131] Starting Up an Exothermic Reaction
[0132] Thus, in one aspect, the present invention provides a method
of starting up an exothermic reaction comprising: [0133] (a)
providing at least two separate reaction trains each comprising at
least one reactor; [0134] (b) providing a common coolant
circulation system which comprises a single common reservoir
comprising a coolant which is fed into each reaction train; [0135]
(c) starting circulation of the coolant to each reaction train;
[0136] (d) increasing the pressure the reactors to a desired
reaction pressure; [0137] (e) feeding a reactant feedstream into
each reaction train; [0138] (f) increasing the temperature of the
single common reservoir while adjusting the GHSV of the reactant
feedstreams through each reaction train to obtain the desired
extent of exothermic reaction.
[0139] The first and second coolants may be the same or
different.
[0140] In an alternative aspect, the present invention provides a
method of starting up an exothermic reaction in a start-up reactor
comprised in a reaction train, said method comprising [0141] a)
providing multiple reaction trains each comprising at least one
reactor; [0142] b) providing a common coolant circulation system
which comprises a single common reservoir comprising a first
coolant which is fed into each reaction train except the reaction
train comprising the start-up reactor in which the exothermic
reaction is to be started up; [0143] c) providing a second coolant
circulation system associated with a second coolant reservoir
comprising a second coolant which is fed into the reaction train
comprising the start-up reactor; [0144] d) increasing the pressure
in the start-up reactor to a desired reaction pressure; [0145] e)
feeding a reactant feedstream into the reaction train comprising
the start-up reactor; [0146] f) running the process until the
operating conditions of the start-up reactor are such that the
coolant exiting the start-up reactor may be reintroduced to the
common coolant circulation system; and [0147] g) stopping the feed
of the second coolant to the reaction train comprising the start-up
reactor while simultaneously initiating a feed of the first coolant
to the reaction train comprising the start-up reactor; [0148] h)
redirecting the first coolant from the reaction train comprising
the start-up reactor to the single common reservoir.
[0149] Some exothermic reactions can initially proceed at a very
high rate releasing a large amount of heat. Such exothermic
reactions may benefit from being carried out in reactors which are
under individual, isolated control during and following start-up of
the exothermic reaction. This individual, isolated control may be
provided by the use of a second coolant circulation system which is
separate from the common coolant circulation system. The use of a
method which provides individual, isolated control to the start-up
reactor allows isolated control of the start-up reactor operating
conditions which may help to prevent thermal runaway during the
initial stages of the exothermic reaction.
[0150] To avoid losses in production from the exothermic reactions
both in the start-up reactor and in the reactors fed by the common
coolant circulation system, the method providing the individual,
isolated control of the start-up reactor may be maintained until
the operating conditions, or the exothermic heat release, of the
start-up reactor more closely match those of the reactors which are
not in the start-up loop, but are instead fed by the common coolant
circulation system. Once this stage has been reached, the start-up
reactor can be reintroduced to the common coolant circulation
system with minimal impact on production.
[0151] When the coolant is a two-phase coolant, the coolant exiting
the start-up reactor may be reintroduced to the common coolant
circulation system when the operating conditions of the start-up
reactor are such that the pressure of the coolant exiting the
start-up reactor is not less than the pressure in the common
coolant circulation system and, optionally, not more than 100 psi
greater than the pressure in the common coolant system.
[0152] This isolated start-up method may be carried out on the
system shown in FIG. 1 as described below.
[0153] As used herein, the term "start-up reactor" is used to
describe a reactor during the time in which an exothermic reaction
is started or initiated.
[0154] The first and second coolants may be the same or different.
The type of coolant used may be the same as the coolants listed
hereinabove.
[0155] The second coolant reservoir may be operated at a
temperature in the range from about 25 to about 300.degree. C.,
from about 100 to about 300.degree. C., or about 200 to about
225.degree. C., or about 200 to about 220.degree. C., or about
205.degree. C. The second coolant reservoir maybe operated at a
pressure in the range from about 100 to about 15,000 kPa, or about
100 to about 8600 kPa, or about 450 to about 4100 kPa, or about 450
to about 3400 kPa, or about 1200 to about 2600 kPa, or about 1200
to 2100 kPa, or about 1200 to about 1900 kPa.
[0156] In one embodiment, where the coolant is water, the second
coolant reservoir may be a second steam drum which is operated at a
temperature in the range from 100 to 300.degree. C., in one
embodiment (for example where the exothermic reaction is a FT
process) 200 to 225.degree. C., or 200 to 220.degree. C., or about
205.degree. C. and a pressure in the range from about 100 to about
8600 kPa, about 100 to about 3400 kPa, in one embodiment, about
1200 to about 2600 kPa, or about 1200 to about 2100 kPa, or about
1200 to about 1900 kPa, or about 1700 to about 1900 kPa.
[0157] In this isolated start-up method, the second coolant
reservoir may operate at a pressure of from about 180 psia to about
250 psia (about 1240 kPa-about 1725 kPa). This pressure is
particularly useful when the exothermic reaction is a
Fischer-Tropsch reaction.
[0158] The isolated start-up method allows the start-up reactor to
be exposed to a temperature ramp to initiate the reaction. The
second coolant reservoir is used to provide the temperature ramp
over a period of 12 to 24 hours. The temperature ramp may involve
increasing the temperature from ambient temperature to between
about 170.degree. C. and abut 214.degree. C., e.g. about
205.degree. C. and about 214.degree. C. These temperatures are
particularly useful when the exothermic reaction is a
Fischer-Tropsch reaction.
[0159] Where the coolant is a fluid (e.g. a liquid) which has a
boiling point lower than the heat generated by the exothermic
reaction, it removes heat from the reaction by undergoing a partial
phase change to provide a two phase coolant. During the temperature
ramp the temperature and pressure of the two phase coolant as it
exits the reactor increases from a starting temperature and
pressure to approximately 205.degree. C. and 250 psia. This
temperature and pressure increase is often seen when the exothermic
reaction is a Fischer-Tropsch reaction.
[0160] Controlling the Reactor Temperature
[0161] In an alternative embodiment, the single common coolant
reservoir method described herein may be provided in a system in
which it is possible to individually control the coolant
temperature in each reaction train. This embodiment provides all of
the advantages associated with the single common coolant reservoir
methods described previously, such as the ability to maximize the
production capacity of a reaction train in order to exploit
economics of scale to minimize unit cost of production. However, in
addition, this embodiment allows for the individual temperature
control of the individual reactors within the reaction trains.
[0162] Accordingly, the present invention provides a method for
removing heat from an exothermic reaction comprising: [0163] (a)
dividing a reactant feed stream into at least two separate reactant
substreams; [0164] (b) feeding each reactant substream into a
separate reaction train which comprises a reactor; [0165] (c)
feeding a coolant stream from a common coolant reservoir into each
reactor; [0166] (d) performing the exothermic reaction in the
reactor to produce reaction products and coolant to which heat has
been transferred; [0167] (e) feeding the coolant to which heat has
been transferred from each reaction train to a single common
reservoir in which the heat is removed from the coolant; [0168] (f)
feeding the coolant from which the heat has been removed in step
(e) back into step (c), wherein: [0169] the coolant is a fluid
which has a boiling point lower than the exothermic reaction
temperature; [0170] the coolant to which heat has been transferred
in steps (d) and (e) is a two phase coolant; and [0171] the
progress of the exothermic reaction in each reactor is controlled
by adjusting the pressure of the two phase coolant.
[0172] Steps (a)-(f) of this embodiment are the same as those
previously described and the details provided above for those steps
apply equally to this embodiment. This embodiment differs only in
its method of controlling the progress of the exothermic reaction
in each reactor.
[0173] As previously discussed, the reactant substream flows along
the reaction train and through the one or more reactors, it is
contacted with the catalyst and the exothermic reaction takes place
(step (d)). The heat generated by the exothermic reaction is
transferred to the coolant, thus removing the heat from the
reaction. Hence, step (d) produces reaction products and coolant to
which heat has been transferred.
[0174] The coolant is a fluid (e.g. a liquid) which has a boiling
point lower than the exothermic reaction temperature. It removes
heat from the reaction by undergoing a partial phase change to
provide a two phase coolant. Consequently, the coolant to which
heat has been transferred in steps (d) and (e) is a two phase
coolant. Where water is the coolant, steam is generated.
[0175] The progress of the exothermic reaction in each reactor may
be controlled by adjusting the pressure of the two phase coolant.
The pressure of the two phase coolant can be adjusted, which, in
turn, adjusts the boiling point of the two phase coolant. This
pressure adjustment takes place downstream of the reactor while the
two phase coolant is still in the reaction train, i.e. prior to
step (e) where the two phase coolant from each reaction train is
fed into a single common reservoir. In this way, the pressure can
be used to control progress of the exothermic reaction in each
reaction train individually. An increase in pressure of the two
phase coolant leads to an increase in boiling point of the coolant.
This allows the exothermic reaction to be conducted at a higher
temperature while maintaining adequate cooling. On the other hand,
a decrease in pressure of the two phase coolant leads to a decrease
in boiling point of the coolant. Consequently, the exothermic
reaction can be conducted at a lower temperature. In this way, the
pressure of the two phase coolant can be used to provide the
appropriate temperature control for the exothermic reaction.
[0176] The pressure of the two phase coolant may be controlled
through the use of a valve, e.g. a backpressure two phase flow
control or by forward flow control.
[0177] In one embodiment, the progress of the exothermic reaction
in a reactor may be controlled by adjusting the pressure of the two
phase coolant and adjusting the flow rate of the reactant substream
through the reaction train of which the reactor forms a part.
[0178] In one embodiment, the progress of the exothermic reaction
in a reactor may be controlled by adjusting the pressure of the two
phase coolant and by adjusting the composition of the reactant
substream which is fed into the same reaction train.
[0179] In one embodiment, the progress of the exothermic reaction
in a reactor may be controlled by adjusting the pressure of the two
phase coolant and adjusting the flow rate of the reactant substream
through the reaction train of which the reactor forms a part and
adjusting the composition of the reactant substream which is fed
into the same reaction train.
[0180] In one embodiment, the progress of the exothermic reaction
in at least one reactor is controlled by adjusting the pressure of
the two phase coolant associated with that at least one reactor,
while the progress of the exothermic reaction in at least one
further reactor may be controlled by adjusting the flow rate of the
reactant substream through the reaction train of which the at least
one further reactor forms a part.
[0181] In one embodiment, the progress of the exothermic reaction
in at least one reactor is controlled by adjusting the pressure of
the two phase coolant associated with that at least one reactor,
while the progress of the exothermic reaction in at least one
further reactor may be controlled by adjusting the composition of
the reactant substream through the reaction train of which the at
least one further reactor forms a part.
[0182] In one embodiment, the progress of the exothermic reaction
in at least one reactor is controlled by adjusting the pressure of
the two phase coolant associated with that at least one reactor,
while the progress of the exothermic reaction in at least one
further reactor may be controlled by adjusting the flow rate of the
reactant substream through the reaction train of which the at least
one further reactor forms a part and the progress of the exothermic
reaction in at least one still further reactor may be controlled by
adjusting the composition of the reactant substream through the
reaction train of which the at least one still further reactor
forms a part.
[0183] This embodiment can also be used in conjunction with the
method for isolating an individual reaction train (described above
and shown in FIG. 1).
[0184] The invention will now be further described by reference to
the following figures and examples which are in no way intended to
be limiting on the scope of the claims.
[0185] FIG. 1 is a schematic representation of a method for
removing heat from an exothermic reaction according to the method
of the invention;
[0186] FIG. 2 is a schematic representation of a method for
removing heat from an exothermic reaction according to the prior
art;
[0187] FIG. 3 is a schematic representation of a method for
removing heat comprising adjusting the flow rate of the reactant
substreams;
[0188] FIG. 4 is a schematic representation of a method for
removing heat comprising adjusting the composition of the reactant
substreams;
[0189] FIG. 5 is a schematic representation of a method for
removing heat comprising adjusting the pressure of the two phase
coolant.
[0190] In FIG. 1, a reactant feedstream (1) is divided into five
reactant substreams which are fed to separate reaction trains (3a,
3b, 3c, 3d, 3e). Each reaction train comprises at least one reactor
(5a, 5b, 5c, 5d, 5e) respectively. A coolant stream (7a, 7b, 7c,
7d, 7e) is fed to each reactor from a common coolant reservoir
(15). The exothermic reaction is performed in each of the reactors
to produce reaction products (11) and coolant to which heat has
been transferred (13a, 13b, 13c, 13d, 13e). The coolant to which
heat has been transferred is passed to a single common coolant
reservoir (15) wherein steam (17) is separated from the coolant
stream (19) which is then fed back into the reactors. The figure
also shows a second coolant system which comprises a second smaller
coolant reservoir (21) from which coolant (23) can be fed and to
which coolant to which heat has been transferred can be fed from a
reaction train (25).
[0191] The method depicted in FIG. 1 can be used to isolate a
reaction train or to carry out the isolated start-up method, both
described in detail above. The second coolant system shown in FIG.
1 can be used to isolate reaction train 3a or alternatively provide
an isolated start-up method in reaction train 3a.
[0192] In FIG. 2, a reactant feedstream (30) is divided into three
reactant substreams which are fed to separate reaction trains (32a,
32b, 32c). Each reaction train comprises at least one reactor. A
coolant stream (34a, 34b, 34c) is fed to each reactor. The
exothermic reaction is performed in each of the reactors to produce
reaction products and coolant to which heat has been transferred
(36a, 36b, 36c). In each reaction train, the coolant to which heat
has been transferred is passed to a coolant reservoir (38a, 38b,
38c) wherein steam (40a, 40b, 40c) is separated from the coolant
stream (42a, 42b, 42c) which is then fed back into the
reactors.
[0193] In FIG. 3, a reactant feedstream (1) is divided into five
reactant substreams which are fed to separate reaction trains (3a,
3b, 3c, 3d, 3e). A means of adjusting the flow rate of each
reactant substream is shown (4a, 4b, 4c, 4d, 4e), which may be a
valve. Each reaction train comprises at least one reactor (5a, 5b,
5c, 5d, 5e) respectively. A coolant stream (7a, 7b, 7c, 7d, 7e) is
fed to each reactor from a common coolant reservoir (15). The
exothermic reaction is performed in each of the reactors to produce
reaction products (11) and coolant to which heat has been
transferred (13a, 13b, 13c, 13d, 13e). The coolant to which heat
has been transferred is passed to a single common coolant reservoir
(15) wherein steam (17) is separated from the coolant stream (19)
which is then fed back into the reactors.
[0194] In FIG. 4, a reactant feedstream (1) is divided into five
reactant substreams which are fed to separate reaction trains (3a,
3b, 3c, 3d, 3e). A means of adjusting the composition of the
reactant substream is shown comprising introducing recycled
reactants (6a, 6b, 6c, 6d, 6e) into the reactant substream. The
proportion of the reactant substream which is made up from recycled
reactants may be controlled by adjusting the flow of the recycled
reactants (8a, 8b, 8c, 8d, 8e), e.g. by the use of a valve. Each
reaction train comprises at least one reactor (5a, 5b, 5c, 5d, 5e)
respectively. A coolant stream (7a, 7b, 7c, 7d, 7e) is fed to each
reactor from a common coolant reservoir (15). The exothermic
reaction is performed in each of the reactors to produce reaction
products (11) and coolant to which heat has been transferred (13a,
13b, 13c, 13d, 13e). The coolant to which heat has been transferred
is passed to a single common coolant reservoir (15) wherein steam
(17) is separated from the coolant stream (19) which is then fed
back into the reactors.
[0195] In FIG. 5, a reactant feedstream (1) is divided into five
reactant substreams which are fed to separate reaction trains (3a,
3b, 3c, 3d, 3e). Each reaction train comprises at least one reactor
(5a, 5b, 5c, 5d, 5e) respectively. A coolant stream (7a, 7b, 7c,
7d, 7e) is fed to each reactor from a common coolant reservoir
(15). The exothermic reaction is performed in each of the reactors
to produce reaction products (11) and a two phase coolant to which
heat has been transferred (13a, 13b, 13c, 13d, 13e). Means for
adjusting the pressure of the two phase coolant is provided (14a,
14b, 14c, 14d, 14e), e.g. valves. The two phase coolant to which
heat has been transferred is passed to a single common coolant
reservoir (15) wherein steam (17) is separated from the coolant
stream (19) which is then fed back into the reactors.
EXAMPLES
Example 1
FT Process
[0196] A reactant feedstream (1) comprising synthesis gas (CO and
H.sub.2) is divided into 5 separate reactant substreams to be fed
to five separate reaction trains (3a, 3b, 3c, 3d, 3e). Each
reaction train comprises 5 reactors arranged in parallel, each of
which contains a fixed-bed of a Fischer-Tropsch catalyst comprising
about 40 weight percent cobalt. The ratio of CO to H.sub.2 in the
reactant feedstream is 0.5. A coolant circulation system comprising
water is provided. The circulation is initiated so that water is
fed from a single common steam drum (15) to the coolant side of the
reactors in each of the separate reaction trains. The water is
partially vaporized into a mixture of water and steam, and is then
recirculated back to the single common steam drum (15). The
temperature and pressure of the single common steam drum is raised
to a temperature of 200.degree. C. and a pressure of 14.5 bar(g) at
which point the 5 reactant substreams are fed at a flow rate of
15,000 hr.sup.-1 to their respective reaction trains such that a
Fischer Tropsch reaction is initiated in each of the reactors. The
synthesis gas reacts in each of the reactors to produce hydrocarbon
products and water. The heat generated by the reaction causes the
circulating water to partially vapourise such that the coolant
leaving the reactor comprises a mixture of water and steam. Once
transferred to the single common steam drum, the water and the
steam are separated. The steam is removed and the water is
recirculated to the reactor trains as described above. Additional
water (9) is added to the recycled water to compensate for the
removal of the steam. The process is operated at a conversion of
70% CO.sub.2. Over time, the activity of the catalyst in each
reactor decreases and it is necessary to reduce the GHSV of the
reactant feedstream into each reaction train to allow for this and
maintain the same level of conversion.
[0197] After the activity of the catalyst in reaction train (3a)
has decreased to an extent that regeneration was necessary,
reaction train (3a) is isolated from the remaining reaction trains
in order to separately regenerate the catalyst. This is done by
first redirecting the partially vapourised water obtained from the
reactors in reaction train (3a) to a second and separate
regeneration steam drum (21). The feed of coolant (7a) from the
single common steam drum to reaction train (3a) is then stopped at
the same time as a feed of water (23) from the second regeneration
steam drum (21) is initiated to reaction train (3a). This is done
over a period of 30 minutes. The pressure of the steam drum (15)
and the pressure of the regeneration steam drum (21) is controlled
to the same pressure during the transition to isolate the reaction
train (3a). After coolant flow from the regeneration steam drum
(21) is established, the regeneration steam drum (21) and the steam
drum (15) may be operated independently. Reaction train (3a) is
then separated from the remaining reaction trains so that
regeneration of the catalyst can be carried out. The pressure of
the regeneration steam drum (21) is set to provide the desired
temperature set point for coolant flow through the reaction train
(3a) during regeneration.
[0198] Following regeneration of the catalyst, reaction train (3a)
is then brought back online by performing the isolation steps in
reverse. More specifically, the coolant feed from the single common
steam drum (7a) is reintroduced to the reactors in reaction train
(3a) while simultaneously stopping the feed of water to the
reactors in reaction train (3a) from the second regeneration steam
drum (23). This is done over a period of 30 minutes. The process is
then allowed to run until the operating conditions of the reactors
in reaction train (3a) match the operating conditions in the
remaining reactors. Once this had been achieved, the partially
vaporized coolant (13a) obtained from the reactors in reaction
train (3a) is redirected to the single common steam drum (15).
[0199] An analogous process is repeated when the catalyst in the
other reaction trains required regeneration.
Example 2
Methanol Production
[0200] A reactant feedstream (1) comprising synthesis gas (CO and
H.sub.2) is divided into 5 separate reactant substreams to be fed
to five separate reaction trains (3a, 3b, 3c, 3d, 3e) (see FIG. 3).
Each reaction train comprises 1 microchannel reactor, each of which
contains a fixed-bed of a Cu/ZnO/Al.sub.2O.sub.3 catalyst. The
reactant feedstream contained 5 mol % CO.sub.2, 26 mol % CO, 64 mol
% H.sub.2 and 5 mol % N.sub.2. The reactant feedstream is fed to
the reactor at 250.degree. C. and 50 bar(g) at 1,500 hr.sup.-1. A
coolant circulation system comprising water is provided. The
circulation is initiated so that water is fed from a single common
steam drum (15) to the coolant side of the reactors in each of the
separate reaction trains. In the reactors, the water is partially
vaporized into a mixture of water and steam, and is then
recirculated back to the single common steam drum (15). The
temperature and pressure of the single common steam drum is raised
to a temperature of 250.degree. C. and a pressure of 39 bar(g).
Once in the reaction train, the flow rate of each reactant
substream may be adjusted individually using automated flow control
valves (4a, 4b, 4c, 4d, 4e) to account for factors such as the
deactivation of the catalyst in the reactor present in that
reaction train.
[0201] The synthesis gas reacts in each of the reactors to produce
methanol. The heat generated by the reaction causes the circulating
water to partially vaporize such that the coolant leaving the
reactor comprises a mixture of water and steam. Once transferred to
the single common steam drum, the water and the steam are
separated. The steam is removed and the water is recirculated to
the reactor trains as described above. Additional water is added to
the recycled water to compensate for the removal of the steam.
Example 3
Isolated Start-Up Method
[0202] A reactant feedstream (1) comprising synthesis gas (CO and
H.sub.2) is divided into 4 separate reactant substreams to be fed
to four separate reaction trains (3b, 3c, 3d, 3e) (see FIG. 1).
Each reaction train comprises one reactor containing a fixed-bed of
a Fischer-Tropsch catalyst comprising about 40 weight percent
cobalt. The ratio of CO to H.sub.2 in the reactant feedstream is
typically from 0.5 to 0.6. A common coolant circulation system
comprising water is provided. During circulation, water is fed from
a single common steam drum (15) to the coolant side of the reactors
in each of the separate reaction trains. The water is partially
vaporized into a mixture of water and steam, and is then
recirculated back to the single common steam drum (15). The single
common steam drum operates at a temperature of about 205.degree. C.
and the coolant temperature at the reactor exit may be between
205.degree. C. and 214.degree. C. The single common steam drum
provides a maximum pressure of 19.7 bar(g) (300 psia or 2068 kPa)
at the reactor coolant exit. The 4 reactant substreams are fed at a
flow rate of between 12,000 hr.sup.-1 and 15,000 hr.sup.-1 to their
respective reaction trains such that a Fischer-Tropsch reaction is
operated at a similar CO conversion in each of the reactors. The
synthesis gas reacts in each of the reactors to produce hydrocarbon
products and water. The heat generated by the reaction causes the
circulating water to partially vaporize such that the coolant
leaving the reactor comprises a mixture of water and steam. Once
transferred to the single common steam drum, the water and the
steam are separated. The steam is removed and the water is
recirculated to the reactor trains as described above. Additional
water (9) is added to the recycled water to compensate for the
removal of the steam. The water may optionally be heated between
the steam drum and the reactors. The process is operated at a CO
conversion in a narrow range, typically from 68% to 72%.
[0203] Regulation of the pressure differential between the reactor
coolant exit and the common steam drum (15) is achieved through the
use of restriction orifices. Between one and five silicon carbide
restriction orifices are positioned on the coolant outlet between
the reactor exit (13b, 13c, 13d, 13e) and the common steam drum
(15) allowing a pressure change in steps up of 10 psi as the flow
path is lined up to a selected orifice or selected orifices thereby
regulating the pressure differential of the coolant between each
reactor and the common steam drum. Water may optionally be heated
to a desired temperature in the range from 205 to 214.degree. C.
between the steam drum exit and the coolant inlet to the
reactor.
[0204] Reaction train (3a) comprises start-up reactor (5a) in which
an exothermic Fischer-Tropsch reaction is to be started up.
Reaction train (3a) is fed by a second coolant circulation system,
also using water as a coolant and associated with second steam drum
(21). The Fischer Tropsch reaction is initiated in start-up reactor
(5a) by increasing the pressure of the start-up reactor steam drum
to 250 psia and starting the reactant substream in reaction train
(3a). The second coolant circulation system is used to increase the
start-up reactor (5a) temperature from ambient temperature to
205.degree. C. over a time of 12 to 24 hours. During this time, the
two phase coolant as it exits the reactor increases from a starting
temperature and pressure to 250 psia and 205.degree. C.
[0205] When the operating conditions of reactor (5a) are such that
the coolant outlet pressure is sufficiently high enough, the
coolant exiting reactor (5a) may be reintroduced to the common
steam drum and coolant from the common coolant circulation system
is introduced into reactor (5a). The coolant feed from the single
common steam drum (7a) is thus reintroduced to the reactor in
reaction train (3a) while simultaneously stopping the feed of water
to the reactors in reaction train (3a) from the second steam drum
(23). Once this had been achieved, the partially vaporized coolant
(13a) obtained from the reactors in reaction train (3a) is
redirected to the single common steam drum (15).
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